	export default (function(designWidth, maxWidth) {
		var doc = document,
		win = window,
		docEl = doc.documentElement,
		remStyle = document.createElement("style"),
		tid;

		function refreshRem() {
			var width = docEl.getBoundingClientRect().width;
			maxWidth = maxWidth || 540;
			width>maxWidth && (width=maxWidth);
			var rem = width * 100 / designWidth;
			remStyle.innerHTML = 'html{font-size:' + rem + 'px;}';
		}

		if (docEl.firstElementChild) {
			docEl.firstElementChild.appendChild(remStyle);
		} else {
			var wrap = doc.createElement("div");
			wrap.appendChild(remStyle);
			doc.write(wrap.innerHTML);
			wrap = null;
		}
		//要等 wiewport 设置好后才能执行 refreshRem，不然 refreshRem 会执行2次；
		refreshRem();

		win.addEventListener("resize", function() {
			clearTimeout(tid); //防止执行两次
			tid = setTimeout(refreshRem, 300);
		}, false);

		win.addEventListener("pageshow", function(e) {
			if (e.persisted) { // 浏览器后退的时候重新计算
				clearTimeout(tid);
				tid = setTimeout(refreshRem, 300);
			}
		}, false);

		if (doc.readyState === "complete") {
			doc.body.style.fontSize = "16px";
		} else {
			doc.addEventListener("DOMContentLoaded", function(e) {
				doc.body.style.fontSize = "16px";
			}, false);
		}
	})(750, 1334);




